Wire pistol

ABSTRACT

The invention relates to a wire pistol comprising a wire feed mechanism including a wire feed pulley rotated by a DC motor and a counterpulley for biasing the wire into engagement with the feed pulley. It is an object of the invention to provide a wire pistol of this type in which, in contrast to prior-art wire pistols, no transmission shift operation or no transmission replacement is required over the entire adjustment range of wire feed rates. This object is attained according to the invention by the provision that the DC motor is adapted to have successive operating voltage pulses of variable pulse width and/or variable pulse frequency applied thereto for thus controlling the wire feed rate. This provision ensures that a sufficiently high torque for the wire feed operation is also available at very low wire feed rates, i.e. at low rotational speeds of the motor.

DESCRIPTION

The invention relates to a wire pistol comprising a wire feed mechanismincluding a wire feed pulley driven by a motor and a counter-pulley forbiasing the wire into engagement with the feed pulley.

A wire pistol of this type is mainly employed in the so-called flamespraying operation. In this application the wire feed mechanism acts toconvey the wire into a gas head having a spray nozzle. In the gas head,which is supplied with a combustible gas in combination with compressedair and oxygen, the combustion of the gas causes the wire material tomelt, the molten wire material being sprayed and expelled through thenozzle together with the combusted gas.

Known wire pistols having a wire feed mechanism suffer from thedisadvantage that the adaptation to wires of different diametersrequires both the feed pulley and the counter-pulley to be exchanged.This exchange operation requires the housing of the wire pistol to beopened and thereafter to be closed again, and is therefore verytime-consuming. This system moreover requires a set of pulleys to bealways held in readiness for the exchange operation.

It is an object of the invention to provide a wire pistol of the typedefined above, in which the adaptation to different wire diameters issimplified and does in particular not require the pistol housing to beopened and does not either require any sets of pulleys to be held inreadiness for replacement.

This object is attained according to the invention by the provision thatthe axis of rotation of the counter-pulley or/and the axis of rotationof the feed pulley is/are adjustable over an adjustment range foradapting the feed mechanism to wires of different diameters.

Thanks to this solution according to the invention, the necessity ofexchanging the feed pulley and the counter-pulley in response to changesof the wire diameter is eliminated, so that the effort for adapting thewire pistol to different wire diameters is reduced. In addition thesolution according to the invention eliminates the necessity of holdingpulley sets in readiness for replacement.

In an advantageous embodiment of the invention, a transmission may beprovided for transmitting the rotation of the feed pulley to thecounter-pulley, the transmission being suitably composed of respectivegears concentrically connected to the feed pulley and thecounter-pulley, respectively. The transmission of the rotation resultsin an increased reliability of the wire feed operation, since thepositively driven counter-pulley itself contributes to the transport ofthe wire.

When employing two gears concentrically connected to the feed pulley andthe counter-pulley, respectively,, the teeth of the gears areadvantageously formed with the reference profile I according to DIN 3972for a number of nine teeth. This configuration of the teeth permits therotation to be transmitted in a slip-free and continuous manner within awide adjustment range of the gear axes.

The counter-pulley may suitably be mounted on a bearing elementconnected by a hinged link to the wall of the housing provided for thewire pistol, and subjected to the action of a pressure engagement deviceoperable to bias the wire into engagement with the feed pulley by way ofthe bearing element and the counter-pulley.

In a particularly suitable embodiment of the invention the bearingelement may be formed as a balance beam carrying the counter-pulley andanother counter-pulley for a detector pulley engaging the wire fordetecting the wire feed rate. The detector pulley engaging the wirepermits the actual value of the wire feed rate to be very accuratelymeasured. This is an important requirement for an effective control ofthe feed rate.

A feed control, particularly a slippage control, can only be achieved bycontrolling the biasing force acting on the wire for engaging it withthe feed pulley. This biasing force may for instance be varied bymounting the pressure engagement device, which may be formed as apressure cylinder with a variable internal pressure, so as to bedisplaceable along the balance beam. The displacement of the point ofattack of the force acting on the balance beam and the variation of thecylinder pressure result in the force transmitted from thecounter-pulley to the feed pulley through the wire.

Further possible embodiments of the invention are apparent from thesubclaims.

Embodiments of the invention shall now be further explained anddescribed by way of example with reference to the accompanying drawings,wherein:

FIG. 1 shows an embodiment of a wire pistol according to the invention,including a gas head for the flame-spraing operation,

FIG. 2 shows an embodiment of a wire feed mechanism of a wire pistolaccording to the invention, including a transmission for transmittingthe rotation of the shows a further embodiment of the wire pistolaccording to the invention.

In FIG. 1, reference numeral 1 designates a motor for rotating a feedpulley 2. The wire is biased into engagement with feed pulley 2 by acounter-pulley 3 mounted on a mounting beam 4. Rotation of the feedpulley causes the wire to be advanced into a gas head 7 provided withgas supply connections 16.

In the present example the axis of the feed pulley is mounted at a fixedposition and extends through the wall of a separate housing provided forthe wire feed mechanism as part of the wire pistol housing. The mountingbeam is adjustably supported relative to the wire. The adaptation todifferent wire diameters is accomplished by adjustment of the pressureengagement device which in the present case is formed as a pressurecylinder acting on mounting element 4, itself formed as a balance beam.

As a result of the fixed position of the axis of the feed pulley, theposition of the longitudinal axis of the wire changes in response tovariations of the wire diameter. In view of this displacement of thewire's longitudinal axis, the gas head 7 is adjustably mounted, in thepresent case secured to housing 5 by means of screws guided in elongateholes and displaceable by means of a rotatable spindle 8. The adaptationof the position of the gas head to varying positions of the wire'slongitudinal axis requires considerably less effort than the formerlyrequired replacement of the feed and counter-pulleys.

With the same facility the adaptation to varying positions of the wire'slongitudinal axis can be accomplished at the opposite housing wall,whereat the wire is guided through a wire guide 10 into the housingprovided for the wire feed mechanism. To this purpose there may beprovided wire guides 10 insertable in the housing wall and formed withpassage bores 9 having a diameter corresponding to the thickness of thewire and a passage bore axis extending in alignment with thelongitudinal axis of the respective wire.

In the present embodiment the balance beam acting as the mountingelement for the counter-pulley has mounted thereon a further pulley 11acting as a counter-pulley for a detector pulley 12. The detector pulley12 serves to determine the actual value of the wire feed rate which maybe supplied to a control device for controlling the wire feed rate. Thewire feed rate is controlled in particular by controlling the forcebiasing the counter-pulley into engagement with the feed pulley tothereby eliminate slippage between between the feed pulley and the wire.In the present example this control function is achieved by theprovision that the internal pressure of the pressure cylinder acting asthe pressure engagement device 6 is variable and the pressure engagementdevice itself is displaceable along the mounting beam, so that the pointof attack of the force acting on the balance beam is variable, as aresult of which the pressure engagement force of the pressure engagementdevice is variably distributed between the feed pulley and the detectorpulley depending on the position of the point of attack.

When the pressure engagement device 6 is mounted for horizontaldisplacement in the longitudinal direction of the balance beam 4, thebottom 21 of housing 5 is suitably formed with dovetail grooves 22 forreceiving correspondingly shaped tongues (not specifically shown)therein. For the adjustment of the pressure engagement device 6 in thehorizontal direction there may then be provided a threaded spindle 23secured to the pressure engagement device 6 and adapted to be adjustedby means of a rotatable adjustment knob 24 mounted at an axially fixedposition in alignment with the spindle on the front face of the housing.The pressure engagement device 6 may also be manually adjustable in asimilar manner, or may even be mounted at a fixed position relative tothe housing 5.

It would also be conceivable to employ a pressure engagement device ofwhich only the pressure engagement force is variable, and which actsonly on the feed pulley through a mounting element and thecounter-pulley mounted thereon.

The feed mechanism shown in FIG. 2 is provided with a transmission fortransmitting the rotation of feed pulley 2a to counter-pulley 3a. Thistransmission of the rotation is effective to increase the reliability ofthe wire feed, particularly in the case of a controlled feed mechanism,due to the fact that the positively rotated counter-pulley contributesdirectly to the wire feed operation.

In the present embodiment the transmission is composed of two camminggears 13 and 14 concentrically connected to the feed pulley and thecounter-pulley, respectively. The camming engagement is maintainedwithin a certain adjustment range of the axis of the counter-pulley. Aslip-free and continuous transmission of the rotation within a wideadjustment range is particularly ensured when the peripheral teeth ofthe gears are formed with the reference profile I according to DIN 3972for a number of nine teeth.

Shown in FIG. 3 is another embodiment of a wire pistol according to theinvention in lateral elevation, parts of the sidewall being broken awayfor affording a view of the diagrammatic illustration of the interiorcomponents, other parts being depicted in section. Disposed on the rearside of the housing 35 is a feed motor 31, while on the opposite endface of the housing a gas head 37 is mounted on the housing 35 foradjustment in the vertical direction in FIG. 3, the adjustment devicestherefor being suitably of similar construction as the adjustmentdevices shown in FIG. 1. Provided on the rear side 41 of the housing isa wire guide 40 with the center axis 42 of a wire (not shown) extendingthrough the wire pistol extending therethrough. For varying the positionof this longitudinal center axis 42 the wire guide 40 may be adjusted inthe vertical direction in a similar manner as the gas head 7, i.e. inthe drawing plane of FIG. 3. Designated at 36 is a gas supply conduitfor the supply of a gas to the gas head 7. The connector nipple 43 maybe used for the introduction of electric leads. The wire feed pulley 32cooperates with a counter-pulley 33. A pair of camming gears 46, 47 (notspecifically shown) are fixedly secured to the axles 44 and 45 of thefeed pulley and the counter-pulley, respectively. Additionally providedare a detector pulley 52 and a further counter-pulley 53. Bothcounter-pulleys 53 and 33 are rotatably mounted on a balance beam 54supported on the one hand on a pressure plunger indicated at 60 andconnected on the other hand by a hinged link 61 to a stationary bearingblock 62 fixedly connected to the housing 35. Link 61 is pivotallyhinged both to bearing block 62 and to balance beam 54.

The pressure engagement device generally indicated at 60 is constructedas follows: Formed in the bottom 63 is a blind bore 64 the open end ofwhich is enlarged to form a bore section 65 of larger diameter.Supported on a shoulder 66 formed between the blind bore and theenlarged bore section 65 is a retaining ring 67 secured in position by acirclip 68. Displaceably guided in blind bore 64 is a piston member 69having an inverted T-shape and sealed against the interior wall surfaceof the blind bore by an O-ring. The stem or plunger 71 of the T-shapedpiston projects upwards through a central opening formed in retainingring 67. Formed in stem 71 to extend in its longitudinal direction is ablind bore 72 whereinto a plunger 73 may be inserted so as to projectupwards from the stem. Disposed between the enlarged portion of theT-shaped piston 69 and the bottom surface of the retaining ring 67 is ahelical spring 74 acting to bias the T-shaped piston downwards in thedirection of the bottom of the blind bore 64. The lower end of the blindbore 64 also communicates with a supply passage 75 for a pressure fluid.

The pressure engagement device 60 is substantially operated to bias thewire to be fed into engagement with the feed pulley for therebyeliminating slippage therebetween by supplying a pressurizing fluid viasupply passage 75. As a result, the T-shaped piston 69 is forced upwardsrelative to the retaining ring 67 against the bias of the spring 74,whereby the balance beam 54 supported on the upper end of the piston israised in the vertical direction until the counter-pulleys 33 and 53 areforced into engagement with the wire (not shown) to be fed. The pressureof the pressurizing fluid supplied to the passage 75 may be varied forcontrolling the thus exerted engagement force.

In the present embodiment the balance beam 4a acting as the mountingelement is connected by a hinged link 15 to the wall 5a of the housingprovided for the wire feed mechanism. For improved guidance of thebalance beam the latter may be formed with a guide hole 18 for theengagement of a guide pin 19 projecting from the housing wall.

I claim:
 1. A wire pistol including a wire feed mechanism, said feedmechanism comprising a motor (1), a wire feed pulley (2) rotated by saidmotor, a detector pulley (12) for monitoring feed rate of a wire, amovable bearing element (4), a first counter-pulley (3) mounted on saidbearing element and disposed to bias the wire into engagement with saidfeed pulley, and a second counter-pulley (11) mounted on said bearingelement and disposed to bias the wire into engagement with said detectorpulley, said bearing element being formed as a balance beam having saidfirst counter-pulley and said second counter-pulley oppositely mountedthereon, and wherein the wire feed mechanism further comprises apressure engagement device which acts on said balance beam in thevertical direction such that said bearing element is adjustable and saidfirst counter-pulley and said second counter-pulley each have an axis ofrotation adjustable over an adjustable range for adapting said feedmechanism to feed wires of different diameters, and wherein saidpressure engagement device (6) is also displaceable along said balancebear in the horizontal direction.
 2. A wire pistol according to claim 1,further comprising a transmission for transmitting rotation of said feedpulley (2) to said counter-pulley (3).
 3. A wire pistol according toclaim 2, wherein said transmission is composed of respective gearsconcentrically connected to said feed pulley (2) and said counter-pulley(3), respectively.
 4. A wire pistol according to claim 3, wherein theteeth of said gears are formed with the reference profile I according toDIN 3972 for a number of nine teeth.
 5. A wire pistol according to claim1, wherein the wire pistol further includes a housing (5), and the wirefeed mechanism further comprises a hinged link (15) connected betweensaid bearing element (4) and the housing (5).
 6. A wire pistol accordingto claim 1, wherein said pressure engagement device (6) is formed as apressure cylinder.
 7. A wire pistol according to claim 1 wherein thewire extends through said wire feed mechanism into a flame spraying gashead (7), and the position of said gas head (7) is adaptable to thevarying position of the longitudinal axis of the wires having differentdiameters.
 8. A wire pistol according to claim 7 wherein the position ofsaid gas head (7) is adjustable by means of a spindle (8).